Oocytes from Xenopus laevis were injected with polysomes from normal human term placenta. Synthesis of the protein hormone Human Placental Lactogen (HPL) in the oocytes was demonstrated by specific immunoprecipitation with anti-HPL serum. Analysis of the immunoprecipitates on SDS-polyacrylamide gel revealed one peak, with a migration distance corresponding exactly to that of [14C]-Radioacetylated HPL added as a marker. Two days after injection the mRNA was still able to direct the synthesis of HPL.